1. Field of Invention
The present invention relates to an integrated surface-emitting optoelectronic module and the method for making the same and, in particular, to an optoelectronic module that utilizes a complete silicon substrate to assemble a surface-emitting optoelectronic device and an optical fiber by passive alignment and the method for making the same.
2. Related Art
Optical alignment plays a very important role in optoelectronic device packaging and can be categorized into two types, namely, active alignment and passive alignment. Past optoelectronic device packaged products mainly employ the active alignment technology. Although the active alignment is featured in a high coupling efficiency, the packaging process is rather time-consuming, forming a defect for mass production. Therefore, optoelectronic module technology researches have been focused on the passive alignment technology in recent years.
Passive alignment of edge-emitting photonic devices has been disclosed in many literatures (see, for example, M. J. Wale, xe2x80x9cSelf aligned flip chip assembly of photonic devices with electrical and optical connections,xe2x80x9d IEEE 40th Electronic Components and Technology 1, (1990) 34-41, etc.). The structure is commonly formed by simultaneously disposing an optoelectronic device and an optical fiber on the same silicon chip and then packaging them by passive alignment, as disclosed in the U.S. Pat. Nos. 5,163,108, 5,182,782, 5,268,066, and 5,436,996. The U.S. Pat. No. 5,420,953 further adds a convergent device between the optoelectronic device and the optical fiber. However, the surface-emitting photonic devices, such as the vertical cavity surface-emitting laser (VCSEL) and the laser-emitting diode (LED), cannot directly use the packaging method for side-emitting photonic devices. Although the passive alignment technology for such devices had been disclosed in the U.S. Pat. Nos. 5,896,481 and 5,259,054, the structure is modularized; that is, the photonic device and the optical fiber are separately disposed and then assembled together. The advantage of this method is that the optoelectronic devices can be directly welded on the substrate in alignment with the optical fiber. Yet, this assembly method still suffers from the problem of nontrivial alignment. The U.S. Pat. No. 5,905,831 proposes another method to solve the problem of VCSEL flip chip assembly; nevertheless, the optoelectronic device and the optical fiber are still separately disposed.
Regarding the packaging of surface-emitting photonic devices, the U.S. Pat. Nos. 4,954,400 and 5,627,931 propose a method to use silicon (Si) to etch a 54.7-degree mirror surface to be a VCSEL or LED reflecting surface. The 54.7-degree mirror surface may not be able to produce total reflection within the optical fiber. Therefore, the 54.7-degree mirror surface is only suitable for the LED but the VCSEL. Although the above patents mention that a 45-degree mirror surface can be used instead, they do not provide an explicit method. One literature also proposes to use a mirror surface to reflect light output from the VCSEL to the optical fiber (J. Heinrich, M. Rode, K. Pressmar, E. Zeeb, xe2x80x9cLow-cost VCSEL-transceiver module for optical data busses,xe2x80x9d Lasers and Electro-Optics Society Annual Meeting, 1997. LEOS ""97 10th Annual Meeting. Conference Proceedings., IEEE 2, (1996) 58-59.), it nevertheless does not mention the manufacturing method and the structure. The U.S. Pat. No. 5,696,862 discloses a packaging technology for surface-emitting lasers. However, the structure is rather complicated and not suitable for mass production. The U.S. Pat. Nos. 5,896,481 and 5,905,831 also propose a modularized surface-emitting photonic device assembly technology. One can see from the above description that the passive alignment for assembling a surface-emitting photonic device and an optical fiber on the same substrate has not had a clear structure yet.
As to making a 45-degree mirror surface on a silicon substrate to reflect incident light from a surface-emitting photonic device with a flip chip, some literatures concerning about mirror reflection suggest to use instead a 54.74-degree mirror surface to reflect light from the optical fiber by the mirror surface to the LED. The 54.74-degree mirror surface is suitable for light-receiving devices but not light-emitting devices (D. J. Sadler, M. J. Garter, C. H. Ahn, S. Koh, and A. L. Cook, xe2x80x9cOptical reflectivity of micromachined {111 }-oriented silicon mirrors for optical input-output couplers,xe2x80x9d J. Micromech. Microeng. 7 (1997) 263-269). Some other literatures propose to use a 45-degree mirror surface as a reflecting surface but do not explain the explicit structure (C. Strandman, L. Rosengren, H. G. A. Elderstig and Y. Backlund, xe2x80x9cFabrication of mirrors together with well-defined V-grooves using wet anisotropic etching of silicon,xe2x80x9d J. Microelectromechanical Systems 4, No. 4 (1995) 213-219).
The known development in 45-degree mirror surfaces is mainly in the silicon chip technology. Conventionally, the optoelectronic packaging mainly etches a V-groove from the Si(100) surface toward the (111) surface, which subtends 54.74 degrees with the (100) surface for accommodating an optical fiber. However, the 54.74-degree surface is not ideal for the reflecting surface of surface-emitting optoelectronic devices when considering the optical transmission path. Furthermore, in spite of the fact that the technology of etching 45-degree mirror surfaces (111) and (110) on the Si(100) surface has been disclosed in many literatures, the actual application in optoelectronic substrates, however, has an important problem. That is, the undercut during wet etching will result in a wider V-groove than the originally designed mask after the etching is completed.
Therefore, it is an object of the invention to provide a substrate structure that employs passive alignment and is free from the packaging problem of surface-emitting optoelectronic devices and the method for making the same.
Pursuant to the above-mentioned object, the invention provides a manufacturing method for an integrated surface-emitting optoelectronic module that utilizes passive alignment to achieve the coupling between the optoelectronic device and the optical fiber. The method comprises the steps of: (1) applying photoresist over a silicon substrate and defining V-groove areas needed for disposing an optical fiber using photolithography procedure; (2) etching a vertical groove in the areas of the V-grooves by dry etching and removing the photoresist afterwards; (3) growing a layer of dielectric on the silicon substrate using a furnace; (4) covering the substrate with photoresist
On the other hand, the invention also provides an integrated surface-emitting optoelectronic module manufactured according to the above method.
According to the disclosed manufacturing method, the procedure further disposes a dielectric layer over the silicon substrate to protect the vertical walls, preventing the groove from getting wider due to subsequent wet etching. The integrated surface-emitting optoelectronic module packages a surface-emitting optoelectronic device and an optical fiber on the same substrate by a flip chip, thus reducing the misalignment problem due to separate assemblies.
Other features and advantages of the present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings.